1. Field of the Invention
The present invention relates to touch sensitive devices. In particular, the present invention relates to a device which responds to the touch of a finger tip to move a cursor, make function commands, or provide control signals to computers or other electrical equipment.
2. Description of the Prior Art
With the ever-increasing popularity of computers, there has been considerable effort expended in developing new devices for interaction between the operator and the computer. At the present time, most of the interaction between the operator and the computer is performed through a keyboard and a display screen.
Functions such as editing and menu selection normally utilize a cursor which appears on the screen and is controlled by an input device. In some computers, movement of the cursor is performed by a set of keys which control movement of the cursor in vertical and horizontal directions on the screen. The use of keys for cursor control, however, is relatively slow and inconvenient.
Joy sticks have also been used for cursor control in computers as well as video games. Joy sticks, however, require movable mechanical parts which tend to wear out with time.
Another form of cursor control which has found increasing popularity is the "mouse", which is a small hand-held device which is moved by hand over a surface and which, as a result of that movement, provides cursor control signals which cause movement of the cursor on the display screen. The mouse also normally contains one or more programmable buttons which allow the operator to select a particular function to be performed as a result of the cursor movement.
At the present time, there are two general types of "mouse" products commonly in use. The first is the mechanical mouse in which a ball or a pair of orthogonal wheels are turned as a result of movement of the mouse over a working surface. The revolutions of a shaft attached to either the wheels or the ball are counted to provide an indication of incremental horizontal and vertical movement. While a mechanical mouse offers relatively high speed and high accuracy cursor movement, it also suffers from a number of disadvantages. In particular, the mechanical mouse has moving mechanical parts which tend to break or wear out. In addition, there is a tendency for dust to be picked up and accumulate in the motion sensing mechanism, which can affect the accuracy of the commanded movements of the cursor and ultimately result in malfunction and failure of the mouse.
The second type of mouse is the optical mouse, which does not require moving mechanical parts. The optical mouse, however, requires a specially designed pad which is marked with a grid of dots or lines. As the optical mouse is moved over this grid, it optically senses the lines or dots of the grid to produce cursor command signals representing X and Y coordinates of the cursor on the display screen. Although there are no moving parts in the optical mouse, it still has drawbacks. First, the movement of the optical mouse over the pad surface can result in wear. In addition, like the mechanical mouse, the optical mouse requires a considerable amount of desk surface in order to operate.
Another type of cursor control device which has been proposed uses an array of membrane switches which respond to the pressure of a finger. This type of pressure sensitive touch control device, however, requires considerable pressure by the operator's finger in order to produce movement of the cursor on the screen, and therefore cannot reliably sense the light sweep of a finger across its surface. This effectively limits the speed of the device.
Other types of cursor control devices have also been used in the past. One of these devices is the touch screen. In this device, the operator's finger can command certain functions or cursor movement by touching selected areas of the screen. One advantageous form of touch screen is described in U.S. Pat. No. 3,636,409 by Norman J. Braaten. In this device, transparent conductive pads are deposited on the surface of the display screen. When a person touches one of the conductive pads, an increase in capacitance occurs which is sensed by the change in frequency of an oscillator circuit. The oscillations corresponding to the various pads are counted and compared to a threshold value to provide an indication of which, if any, of the pads has been touched.
While the touch screen has proved to be very effective in many applications, it too has some drawbacks. In particular, the touch screen requires that the operator lift his arm in order to touch the screen. This can result in fatigue if done for a long period of time. In addition, the touching of the screen with the operator's finger can result in the screen surface becoming smudged over a period of time.
There is a continuing need for improved cursor controllers which are relatively compact, accurate and easy to use.